1. Field of the Invention
The present invention relates to a digital broadcasting system, and more particularly, to a method and apparatus for reproducing digital broadcasting.
2. Description of the Related Art
In current digital video broadcasting systems, analog audio and video signals are converted into a digital signal to be transmitted and the transmitted signal is received in a receiver to be converted again into analog signals. In this case, in order to transmit more digital data to a given channel capacity, the digital audio and video data are respectively compressed by a compression algorithm to be transmitted in the form of a bitstream. In the receiver, the compressed digital data is decompressed so as to restore the data to the original digital audio and video data.
In general, with digitalization, image compression technology is used as a main element to support multimedia. Among the image compression technology, Moving Picture Expert Group-2 (MPEG-2) is an international standard for compression decoding of digital moving pictures, the compression decoding being the main technology in a multimedia environment.
When an audio/video multi bitstream is input to a digital broadcasting receiver employing MPEG-2, the digital broadcasting receiver separates audio data and video data from a transport demultiplexer. The separated video data and audio data are respectively input to a video decoder and an audio decoder generally in the form of a packetized elementary stream (PES).
Since the digital broadcasting receiver uses a digital signal, unlike analog systems, additional A/V lip-synchronization is needed to synchronize a video signal with an audio signal. A general A/V lip-synchronization is formed by using a presentation time stamp (PTS) and a system time clock (STC) given each time video data and audio data are decoded and reproduced.
More specifically, an audio decoder and a video decoder include the PTS that corresponds to each frame and thus the PTS is compared with the STC of the same system, thereby controlling A/V lip-synchronization. If the PTS is in a specific range set previously based on the STC, A/V lip-synchronization is determined to be correct and a normal decoding is performed to output A/V data. However, if the PTS is not in a specific range set previously based on the STC, decoding is skipped or A/V lip-synchronization is corrected through repeating or waiting.
As described above, if the PTS that corresponds to each frame of audio data and video data exists, AV lip-synchronization can be well accomplished. However, if the PTS that corresponds to each frame of audio and video does not exist, the time to display the corresponding frames may be inaccurate since there is no PTS that can be compared with the STC and thus AV lip-synchronization may not be accomplished well.